The ornamental design for a thigh-high stocking, as shown and described.
FIG. 1 is a front perspective view of a thigh-high stocking;
FIG. 2 is a side elevation view thereof; and,
FIG. 3 is a front elevation view thereof.
The broken line showing in the drawing figures is environmental subject matter included to show how the claimed design may appear when worn and forms no part of the claimed design.